This proposal seeks support for upgrading a fluorescence activated cell sorter from a single to a dual laser instrument. The cell sorter is located at the Flow Cytometry Facility of the University of Iowa. The administration of this upgrade would be by the director of the facility and the Flow Cytometry Advisory Committee. This is the only cell sorter in the state. It currently supports users throughout the University including the medical and dental schools. Since this instrument, a Becton-Dickinson FACS IV, was acquired almost five years ago, the needs of its users have increased. A dual laser instrument would increase this productivity, allowing them to reach experimental objectives of their ongoing research projects which would otherwise be difficult, to take full scientific advantage of unanticipated developments in their projects, and to develop potentially significant new findings. Such an upgrade is thus strongly needed to support ongoing research projects in NIH supported laboratories. The advantage of such a system is that it would allow the use of a greater range of cellular staining reagents simultaneously. This would greatly increase the range of correlated cellular properties that could be measured. In the past two years, a burst of activity in developing new cellular staining reagents has occurred. Reagents now exist to measure diverse cellular properties such as transmembrane potential, calcium content, intracellular pH, chromosome structure and banding characteristics, various cellular enzymatic activities, cell cycle status, membrane proteins, including receptors, and differentiation markers, and other cellular properties. A dual laser system would facilitate the simultaneous measurement of such properties so that they could be correlated on a per cell basis. This would greatly facilitate ongoing studies in cell biology, cellular immunology and endocrinology, and oncogenesis.